Microorganisms and Microbiology

Updated Fall 2015Jerald D. Hendrix

Historical Background

A. Discovery of microorganismsB. Spontaneous generation vs. BiogenesisC. Pure culture techniqueD. Significance of microbes

A. Discovery of Microbes

Anton van Leeuwanhoek– Mid-1600s– Developed early microscope– First to observe microbes:

“animicules”– Did not appreciate the

significance or impact of microbes on human life

B. Spontaneous Generation vs Biogenesis

Aristotle– Suggested that mice could develop by spontaneous

generation

Redi– Mid-1600s– Experimentally demonstrated that maggots (fly

larvae) do not develop via spontaneous generation

B. Spontaneous Generation vs Biogenesis

Needham vs Spallanzani– Mid-1700s– Spallanzani demonstrated that microbes do not

develop by spontaneous generation in sterile nutrient media sealed in flasks

– Needham criticized Spallanzani’s work: asserted that spontaneous generation required fresh air in the flask

B. Spontaneous Generation vs Biogenesis

Pasteur– Mid to late-1800s– French chemist and a “founder” of the modern

science of microbiology– Settled the Spallanzani-Needham debate with the

“swan-necked flask” experiment– Worked on many important problems in

microbiology, most notably in vaccine production– Aseptic technique

B. Spontaneous Generation vs Biogenesis

Tyndall– Late 1800s– Demonstrated directly that the growth of microbes in

contaminated flasks was due to microbial cells from airborne dust particles, not from spontaneous generation

– Developed a method (tyndallization) to ensure sterilization of media through repeated boiling

C. Pure Culture Technique

Pure culture– A sample of microbial growth that contains only a

single species– Challenging to obtain because of the large numbers

and small sizes of microbesEarly attempts– “Limiting dilution” method in broth medium used by

Pasteur and others– Difficult to ensure that a single species exists in the

culture

C. Pure Culture Technique

Streak plate method– Developed in the 1870s by Koch and his co-workers– The objective: to obtain isolated colonies – spots of

microbial growth that come from a single parent cell– The method: streak the sample on semisolid

medium, containing a gelling agent– Agar: the most commonly used gelling agent

C. Pure Culture Technique

C. Pure Culture Technique

D. Significance of Microbes

1. Microbes and disease: late 1700s – late 1800sJenner – small pox vaccineSnow – epidemic control via public health measuresSemmelweis – importance of hand-washingLister – antiseptic surgical methodsPasteur – rabies vaccineKoch – isolated anthrax and tuberculosis bacteria; Developed Koch’s postulates

D. Significance of Microbes

2. Microbes and the environment: late 1800sWinogradsky, Beijerinck, and others: established the role of microbes in biogeochemical cycling

3. Twentieth century microbiologyPublic health microbiologyDiscovery of virusesAntimicrobial chemotherapyMicrobial cell structure and biochemistryMicrobial genetics and genetic engineering